Animal Waste, Water Quality and Human Health

Zoonotic waterborne pathogen loads in livestock 873.3.1.2 Faecal shedding of E. coli O157:H7 by livestockWhile studies have reported isolation of E. coli O157:H7 from a number ofdomestic and wild animal species, ruminants, in particular cattle, are consideredthe primary reservoir of this important human pathogen (Dunn et al. 2004;Gunn et al. 2007; Khaista et al. 2006; Hancock et al. 1997a, 1997b, reviewed inRenter & Sargeant, 2002, Renter et al. 2004). The importance of cattle as areservoir is underlined by the high prevalence of the organism in the species.Serological evidence suggests that all beef cattle herds in the USA have beeninfected with the organism at one time or another (Laegreid et al. 1999). Aswell, many fattened cattle at slaughter can be shedding the organism in theirfaeces (van Donkersgoed et al. 1999, Elder et al. 2000). There is a strongepidemiological link between both sporadic cases and outbreaks of humaninfections and the consumption of undercooked beef and other foods, includingvegetables, unpasteurized milk and fruit juices and water contaminated withruminant faeces (Gyles 2007, Karmali et al. 2009). Recently, Walters et al.(2007) have also reported that the presence of the Bacteroides ruminant faecalmarker in surface water is significantly higher in samples from which E. coliO157:H7 was isolated.In cattle, calves become infected with the organism shortly after birth followinga spike in peri-parturient shedding of the organism in their dam’s faeces (Gannonet al. 2002). In the study, from 2 to 18% of dams and 23 to 26% of calves wereshown to shed E. coli O157:H7 in their faeces in the period immediatelyfollowing parturition. Many calves continue to shed the organism as they grow;there appears to be a secondary spike in shedding of the pathogen followingweaning which is followed then by a decline through the fattening period (Smithet al. 1997). Elder et al. (2000) reported that 72% of lots of slaughter cattle and28% of individual cattle in the Midwestern USA shed E. coli O157:H7 in theirfaeces during July and August. However, these likely represent high values asthere is a seasonal peak in the frequency of shedding of the organism by youngcattle during the summer months (van Donkersgoed et al. 1999). The lowestprevalence is found among adult cattle during the winter months.When this bacterium infects cattle, it colonizes lymphoid-associated epithelialcells in the recto-anal junction using a type III secretion system which encodes anadhesin and a syringe-like apparatus which injects an adhesin receptor as well asa number of intracellular effector proteins into the cells. This changes the cells’morphology and physiology and allows E. coli O157:H7 to attach to them(Kenny 2002, Karmali 2004, Spears et al. 2006). These colonization proteinsshow promise as targets of vaccines to reduce faecal shedding of the organismby cattle.